1. Field of the Invention
The present invention relates to an antenna unit and a watch having the antenna unit.
2. Description of the Related Art
An antenna unit for transmitting and receiving a radio wave is provided in an electronic apparatus such as a radio apparatus and a radio controlled watch. One type of conventional antenna unit as described in Japanese Patent Application KOKAI Publication No. 6-350324 includes an antenna main body, which is formed by metal plate having electrical conductivity, such as brass or copper plate, and which is plated with nickel. And, another type of conventional antenna unit includes a core portion, and a winding portion, which is formed by a coil wound on the insulating tape on the core portion.
When the core portion is formed by material, for example ferrite, having high magnetic permeability and high electrical conductivity, in the latter type of conventional antenna unit, there is a case that an electric current generated in the winding portion when the conventional antenna unit receives radio wave flows in the core portion thereby decreasing radio receiving efficiency of the conventional antenna.
In order to prevent such a drawback as described above from generating in the latter type of conventional antenna unit, an electrically insulating tape is wound on the core portion and the winding portion is formed by the coil wound on the insulating tape on the core portion. And, the insulating tape electrically insulates the winding portion from the core portion.
However, since the insulating tape wound on the core portion has a thickness of about 200 μm and makes its diameter being relatively large, the coil wound thereon needs a relatively large length and decreases its direct-current resistance characteristic, etc. In a case that the core portion has flanges for positioning the coil wound on the core portion at its both ends, the large diametrical insulating tape and the large diametrical coil needs to make the sizes of each flange increase so that the strength of each flange decreases.